This invention relates to a sample cup for use in holding specimens for spectrochemical analysis and, more particularly, to a sample cup including an annular collar having an integrally molded thin film therein.
Sample cups for spectrochemical analysis are used in the prior art to hold or contain liquid, solids, and powdered specimens under normal atmospheric pressures, gas pressures, or in vacuum for analysis such as energy and wave length dispersive techniques and optical emission methods. Such cups, as indicated, are in widespread use.
Essentially, the sample cup consists of three components, a cup-shaped cell having a closed bottom and an opened top, an annular collar, and a snap-on ring. Typical prior art cups are shown in U.S. Pat. No. Des. 238,693 entitled "Cell for X-Ray Spectroscopy or Similar Article" issued on Feb. 3, 1976 to Monte J. Solazzi and U.S. Pat. No. 4,409,854 entitled "Sample Cup with Venting Means for Use in X-Ray Spectroscopy" issued on Oct. 18, 1983 to Michael C. Solazzi, and assigned to the assignee herein.
The collar and the snap-on ring serve to secure a sheet of plastic material such as MYLAR, the trademark for a polyester film sold by E. I. duPont de Nemours and Co., to cover the opened top of the cell when the hollow of the cell is filled with a specimen such as a liquid, solid, or powdered material to be analyzed. Such cells are available from many sources including the assignee Chemplex Industries, Inc., of 140 Marbledale Road, Eastchester, N.Y. 10707.
For spectrochemical analytical investigation of specimens characterized with high abrogation properties in air, the entire assembled sample cup with the plastic sheet covering the top may be then placed within a vacuum or an inert gas environment. Under conditions where pressure equalization is not implemented, the plastic sheet will distend or bow outwardly due to the vacuum or lower pressure. This then places the surface of the sheet closer to the excitation source which may be an X-ray tube or other device. The surface of the sheet of plastic is commonly defined as the sample plane. A variation in the distance from the sample plane to the source of excitation operates to alter the intensity of the characteristic radiation of the specimen and also the intensity of radiation impinging upon the sample from the excitation source. The variations result in erroneous quantitative data and hence cannot be tolerated. As indicated, for applications in a vacuum environment, the thin plastic film distorts or bows out (convex), which decreases the distance from the sample to the excitation source. For applications in a gaseous environment (positive pressure), the thin plastic film tends to be drawn into the hollow of the cell or provides a concave surface. This effect increases the distance between the sample plane and the excitation source. Based upon the distortions of the thin film, the results or analytical data obtained can be of a higher or lower value than would be expected without distortion.
Moreover, it has been found when using the thin plastic sheet that problems arise with tautness of the sheet and, further, with wrinkles being formed in the sheet during operation. It has also been found that when attempting to fasten the thin film material to the sample cup, there is a tendency for the side of the opened top portion of the cup to rip the thin sheet material. Thus the prior art uses of thin plastic sheets are not convenient ways of providing a closure for the sample cup.
It is therefore an object of the present invention to provide an improved sample cup including an annular collar which has an integrally formed thin plastic film therein which enables an operator to conveniently fill and assemble the sample cup therefore eliminating the need for the separate attachment of a thin-film sample support material and the corresponding collars to position it correctly.